Impacts of land use and climate change on diversity patterns of leaf litter
arthropods in Xishuangbanna: Insights from metabarcoding and implications for
conservation
Introduction
Forest conversion to other land use types, especially agricultural monocultures, represents
the most significant threat to local and regional biodiversity due to increased extinction
risk, considerable modification of habitat characteristics and creation of new ecological
boundaries. Xishuangbanna (22°00′N 100°48′E) is an autonomous prefecture in
Southwest China situated on the northern edge of tropical Southeast Asia and lies within
the Indo-Burma biodiversity hotspot. The region represents only 0.2% (1.9 million ha) of
China’s total area, but supports approximately 5000 described species of angiosperms
(including the transitional flora of temperate China and tropical Southeast Asia) and an
estimated 16% of China’s total higher plants. Once biologically rich with continuous
tropical rainforests, the region’s land cover is now fragmented and degraded with the
most prominent change caused by forest conversion to agriculture, especially the
plantation of rubber. Habitat fragmentation in agricultural landscapes leads to natural and
semi-natural habitat loss and immediate loss of species that increases extinction risk.
However, it is still largely unknown if and how land use and climate change in
Xishuangbanna affect arthropod communities in natural forests and monoculture
plantations. Conversion of natural forests to monoculture plantations changes the
biophysical conditions required for arthropod growth, reproduction and survival. These
changes have negative consequences on arthropod diversity and composition and result in
increased extinction risk.
Specific objectives
•
To project the effects of land use change on leaf litter arthropod diversity and
community composition
•
To measure the conservation value of natural forests versus monoculture (rubber
& tea) plantations
•
To determine the management treatments that are most successful in restoring
endangered tropical ecosystems and maintaining high arthropod biodiversity
•
To evaluate the minimum patch size of natural forests required to sustain
maximum arthropod biodiversity
General hypotheses
1. Conversion of natural forests to monoculture plantations would result in loss
of arthropod species.
2. The loss of arthropod species is expected to be related to
•
biophysical factors (e.g. vegetation structure, microclimate, litter characteristics)
•
management practices (e.g. fertilizer application, pest control, cutting of
understory vegetation)
Materials and methods
Arthropod sampling
Leaf litter arthropods will be collected from 5 paired sites in Menglun on a monthly basis
for 12 months (Jan – Dec 2014) and from 30 paired sites across Xishuangbanna in June
and July 2014. The study sites chosen include; natural forests (henceforth Forest), rubber
plantations (henceforth Rubber) and tea plantations (henceforth Tea). In each site, nine
leaf litter samples separated 10 m apart (1 in the middle and 2 each in the north, east,
west and south directions) for Winkler will be obtained by placing 1 x 1 m PVC frames
on the Forest, Rubber or Tea floor. The leaf litter and loose humus from within the frame
area will be collected into a litter reducer (without disturbing the top soil) and sieved
through a 0.6 x 0.6 mm mesh wire to separate arthropods from larger leaf litter materials.
The resulting siftate (arthropods plus leaf and soil debris) will be transported to the
laboratory in small polythene bags, where they will be transferred into coarse-mesh bags.
The coarse-mesh bags will be subsequently suspended inside Winkler bags suspended
over a collecting bottle containing 95% alcohol. The Winkler bags will be left to dry for 3
days (72 hours) at room temperature and pressure.
Sample processing and data analysis
Traditional methods of measuring and assessing arthropod community composition and
diversity are time consuming, unreliable and require high expertise. Metabarcoding
represents a powerful tool for biodiversity conservation and ecosystem management at
the organismal to community level because it is more comprehensive, faster, reliable, and
less dependent on taxonomic expertise. It is a fast biodiversity monitoring approach that
integrates DNA taxonomy and high throughput DNA sequencing. This project takes
advantage of robust, established arthropod sampling methodologies in addition to
implementing recent high-throughput technologies using short DNA sequences to
distinguish and assign taxonomies to individual arthropod species. Emerging
technologies including DNA extraction, PCR amplification and pyrosequencing will be
used to prepare samples, extract, amplify, and purify DNA, and post quality control of
sequences. In order to denoise and cluster the sequences into Operational Taxonomic
Units (OTUs), we will apply existing experimentally validated methods.
Responsibilities of the intern
1. Sample collection: S/He might assist with leaf litter arthropod collection from the
field sites around Xishuangbanna (Optional).
2. Arthropod sorting: During the 72 hrs of Winkler incubation, arthropods, some leaf
litter and soil debris fall into the collecting bottle. S/He will be required to assist
with sorting arthropods from the remaining debris (leaf litter and soil). It takes a
day or less to sort a single sample (one site) usually.
3. Arthropod photographing: Since we’re not immediately interested in the identity
of each arthropod species, because we’re going to DNA barcode (COI gene) them
anyway, s/he will assist in taking photographs of all the arthropods in a sample.
4. DNA extraction: The photographed arthropods (from each site) will be crushed
together and their DNA extracted. S/He will assist with DNA extraction from
mass arthropod samples.
5. DNA amplification: S/He will assist with running the polymerase chain
reaction (PCR), a biochemical technology in molecular biology to amplify a
single or a few copies of a piece of DNA across several orders of magnitude,
generating thousands to millions of copies of a particular DNA sequence.
Note: All equipment required in each of the 5 sections mentioned above are available
in our molecular lab or the XTBG Biogeochemical Lab. The intern is not obliged to
use his/her personal equipment in the project during the internship.